Abstract. Here we characterize a highly efficient approach for protein confinement and enzyme immobilization in NH₂– or HOOC– functionalized mesoporous silica (FMS) with pore sizes as large as tens of nanometres. We observed a dramatic increase of enzyme loading in both enzyme activity and protein amount when using appropriate FMS in comparison with unfunctionalized mesoporous silica and normal porous silica. With different protein loading density in NH₂–FMS, the negatively charged glucose oxidase (GOX) displayed an immobilization efficiency (I_e, the ratio of the specific activity of the immobilized enzyme to the specific activity of the free enzyme in stock solution) in a range from 30% to 160%, while the same charged glucose isomerase (GI) showed an I_e of 100% to 120%, and the positively charged organophosphorus hydrolase (OPH) exhibited I_e of more than 200% in HOOC–FMS. The enzyme–FMS composite was stained with the charged gold nanoparticles and imaged by transmission electron microscopy (TEM). Fourier transform infrared (FTIR) spectroscopy showed no major secondary structural change for the enzymes entrapped in FMS. Thanks to the large, rigid, open pore structure of FMS, the reaction rate and K_m of the entrapped enzymes in FMS were comparable to those of the free enzymes in solution. In principle, the general approach described here should be applicable to many enzymes, proteins, and protein complexes since both pore sizes and functional groups of FMS are controllable.

Print publication: Issue 22 (28 November 2006)
Received 24 July 2006, in final form 8 September 2006
Published 25 October 2006